Field of the Invention
The present invention relates to a transparent electroconductive film with a protective film.
Description of the Related Art
A transparent electroconductive film including a film substrate, and an optical adjustment layer and a transparent conductive layer formed on one main surface of the film substrate has been heretofore known. Transparent electroconductive films are used in touch panels and so on. As one example of a method for improving scratch resistance of a transparent electroconductive film, an optical adjustment layer is formed by a dry film formation method, typically a sputtering method. Typically, a transparent electroconductive film is produced by a roll-to-roll method in which layers are continuously formed on a long film substrate.
The transparent electroconductive film, which is wound in the form of a roll, is cut in the form of a sheet having a predetermined shape and size, and subjected to a heating treatment for crystallizing the transparent conductive layer. Thereafter, the transparent electroconductive film may be post-processed for forming fine wiring by patterning or etching. In this connection, Japanese Patent No. 5245893 discloses a technique in which a protective film is provided on the other main surface of the film substrate for facilitating the handling of a sheet of the transparent electroconductive film.
However, a sheet of the transparent electroconductive film with a protective film, which is excellent in scratch resistance, has a problem that curl (warp) is developed with time after the heating treatment, and the curl grows gradually. When the curl grows, it becomes difficult to handle a sheet of the transparent electroconductive film with a protective film in a process for production of a touch panel device (e.g. a step of heating and crystallizing a transparent conductive layer and a step of bonding to other materials). Since conventional touch panels are mostly used in applications of small devices, typically mobile phones, curl is commonly evaluated with a sheet having a small size (e.g. 10 cm×10 cm), and a problem with curl is not obvious. In recent years, however, curl is apt to be developed on a larger scale with as increase in size of touch panels (to, for example, A4 size or larger), and thus a problem with curl is obvious. For example, there may be cases where, as a result of cutting the same transparent electroconductive film with a protective film to a size of 10 cm×10 cm and a size of 50 cm×50 cm and evaluating curl for each of the sheets, curl in the sheet with a size of 10 cm×10 cm is at a sufficiently low level (e.g. 5 mm), whereas curl in the sheet with a size of 50 cm×50 cm is very large (e.g. 20 mm).
On the other hand, there has been heretofore a transparent electroconductive film including an optical adjustment layer formed by a wet film formation method, typically a coating method. A transparent electroconductive film including an optical adjustment layer formed by a wet film formation method is almost free from the above-mentioned problem with curl even when provided with a protective film similar to that described above. However, a transparent electroconductive film including an optical adjustment layer formed by a wet film formation method has a problem of poor scratch resistance. Accordingly, a transparent electroconductive film which has high scratch resistance and which is free from a problem with curl is desired.